Sesquiterpenes phytotoxins

L. maculans isolates Laird 2 and Mayfair 2 (virulent on brown mustard but not on canola) produced in a chemically defined medium the host-selective phytotoxin depsilairdin (8) (Fig. 9.2), containing a novel amino acid residue ((25,35,45)-3,4-dihydroxy-3-methylprolyl) and a sesquiterpene moiety (lairdinol A, synthesized recently [25,26]). Depsilairdin (8) caused disease symptoms similar to those caused by the pathogen on brown mustard, that is, strong necrotic and chlorotic lesions, but no lesions on canola. 

Sesquiterpenes containing either a methylene-y-lactone or a cyclopentenone moiety can react with thiol groups to form a covalent linkage. If the thiol group is on a key enzyme, interaction with artemisinin could inactivate the enzyme, disrupting metabolism. Cysteine is a good antidote for artemisinin as a phytotoxin, but there is no evidence that it is due to a direct interaction of the two molecules.15... 

Catalytic cycloadditions of carbenes to alkenes is a straightforward method for synthesizing cyclopropanes [40]. In fact, cyclopropanes are present in a variety of natural products [41-43]. For example, they occur in some unusual amino acids, in natural phytotoxins such as coronatine, as well as in marine terpenes [44], sesquiterpenes [45], cyclosteroids [46-47] (as part of the A-cycle) or in the side chain of steroids [48]. 

Rodrigues et al. (149) reviewed the biological activities, as well as the structure and occurrence, of the sesquiterpene lactones. The biological activities discussed were anti-cancer, cytotoxic, antibiotic, chemophylaxis (against schistosomiasis), allergic contact dermatitis, antifeedants for insects, vertebrate poisons, and phytotoxins. The structural requirements for biological activity in these compounds were elucidated. Kuksis et al. (96) used GLC to study phytosterolemia. 

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